In the cervical spine, the average cervical disc is approximately 5-9 mm tall when healthy in an adult of normal stature. Presently, the screws for use in fixating into the cervical vertebral bodies are generally of a diameter of 4-5 mm each and have enlarged head portions for retaining them in the fixation device. Thus, these screws when placed in opposition and vertically aligned would have a combined height that exceeds the height of almost all cervical discs.
Implants of the related art have extended the height of the trailing end of the implant to make it taller than the disc space. An example of this is a flanged implant. The flanged implant makes it possible to place screws so that they can be vertically aligned and have sufficient structure of the implant to retain them. The flanged portion of the implant extends outside of the disc space.
In known interbody spinal fusion implants there have been problems with loosening and backing out of screws into the patient""s throat area. These occurrences generally require further surgical procedures to replace the implants and screws entirely, and to repair any damage that may have been caused.
There is a need for an implant having a locking mechanism that can be easily and reliably locked in place to prevent the loosening of and backing out of the bone screws used to attach the implant to the vertebrae in the anterior aspect of the cervical, thoracic, and lumbar spine.
The present invention is directed to an interbody spinal fusion implant having an interbody portion for introduction into a disc space between adjacent vertebral bodies and a flanged portion that extends outside the disc space to overlie at least a portion of the anterior aspect of the vertebral bodies to be fused proximate that disc space. The flanged portion is configured to receive at least two opposed bone screws. The flanged portion includes at least one locking mechanism for locking the bone screws to the implant. At least one of the bone screws is directed into one of the adjacent vertebral bodies and at least another of the bone screws is directed into the other of the adjacent vertebral bodies for securing the implant to the adjacent vertebral bodies. The bone screws have a leading end, a shaft, threading upon the shaft, and a trailing end. The implant and the trailing end of the bone screw are adapted to cooperatively engage each other so as to prevent further advance of the bone screws through the implant. The flanged portion of the spinal implant of the present invention with the screws inserted is low profile so that the bone screw trailing ends do not substantially protrude from the flanged portion so as to not endanger the patient""s overlying tissues, adjacent vessels, and neurological structures.
The bone screws are locked to the flanged portion by a locking mechanism so that the bone screws cannot get loose and/or migrate. The locking mechanism can be a single locking mechanism for locking only one screw to the flanged portion of the implant or a multilocking mechanism for locking two or more screws simultaneously to the flanged portion of the implant. For example, the multilocking mechanism can be a dual locking mechanism for locking two screws to the flanged portion of the implant or a locking mechanism for locking four bone screws to the flanged portion of the implant.
In the various embodiments of the present invention, the locking mechanisms and flanged portion may be configured to either rigidly capture the bone screws so that their positions are fixed, or alternatively allow for the screw angles to be variable in which case the screw angles may remain variable or be fixed when locked.
The flanged implants of the present invention may be configured so that the leading end is a portion of a circle; and where the depth of the implant is sufficient, the leading end is half of a circle; and where the depth of the implant is sufficient, the implant may have generally parallel side walls defining an implant width equal to the diameter of that circle.
In a preferred embodiment of the flanged implant of the present invention, the flanged portion has at least two bone screw receiving holes located at different distances from the mid-longitudinal axis of the implant. Such a configuration permits two such implants can be placed in successive levels of the spine without the bone screws of one implant interfering with the bone screws of the other.
A preferred method of the present invention for inserting a flanged implant at least in part between adjacent vertebral bodies adjacent a disc space and in part along the anterior aspects of the vertebral bodies includes preparing a recipient socket across the disc space and into the adjacent vertebral bodies and locking at least one of the bone screws to the implant.
Another preferred method of the present invention for inserting a flanged implant at least in part between adjacent vertebral bodies adjacent a disc space and in part along the anterior aspects of the vertebral bodies includes preparing a recipient socket across the disc space and into the adjacent vertebral bodies wherein the socket corresponds in shape to the shape of the interbody portion of the flange implant.
Although a preferred embodiment of the present invention has been shown for use in the cervical spine, the flanged implants of the present invention may be used in the thoracic and lumbar spine from the anterior aspects. While the above-described configurations are preferred for various advantages, they do not in any way limit the breadth of the present invention which is limited only by the claims.